Receiver with control of selectivity through variation of the coupling



July 8, 1941.

F. KREIENFELD RECEIVER WITH CONTROL OF SELECTIVITY THROUGH VARIATION OF 'IHE COUPLING I Filed Dec. 24, 1937 N v E N TO R FRIEDRICH ARE/H/FEZD jk y. 7

ATTORNEY Patented July 8, 1941 UNITED STATES PATENT OFFICE RECEIVER WITH CGNTROL F SELECTIVITY THROUGH VARIATION OF THE COUPLING corporation of Germany Application December 24, 1937, Serial No. 181,507 In Germany December 24, 1936 3 Claims.

It is known to control the selectivity of a receivcr by varying the coupling. The varying of the coupling can be carried out for instance by coupling a tube at a higher or lower coupling degree to the following oscillatory circuits. An advantageous mode of execution resides in coupling with each other at a higher or lower degrce two oscillatory circuits tuned to the same frequency whereby the band width will be iniiuenced Without varying the steepness of the flanks of the curve.

The invention is concerned with increasing the range of control towards the side of the smallest band width without decreasing thereby the ampliiication.

The invention resides in that in a receiver with control of the selectivity, the arrangement for varying the coupling and an arrangement for controlling the feedback are so coupled by Way of varying the degree of coupling, more especially the coupling of two oscillatory circuits, that the feedback increases at a looser coupling state.

The invention will be explained in greater detail in the following, with the accompanying figures serving as examples.

Figures 1 and 3 show physical arrangements of the coils in the invention,

Figure 2 shows a circuit employing the invention.

Figure 1 shows a structure and Figure 2 th appertaining circuit. The oscillatory circuits are coupled to each other at a higher or lower degree, by moving the coupling coil K relative to the coil L1. The coupling coil K is mounted in conjunction with the feedback coil R, on a tube I consisting of insulating material. This tube i can be moved on the tube 2 from the outside by means of the lever H and rod S. At the downward movement, the coupling between the coil L2 and feedback coil R becomes looser. The dimensions are so chosen that at the closest coupling of the coils K and L1 the feedback coil has not as yet moved beyond the center of the distance between the coils L1 and L2. At an upward movement, the coupling conditions vary in the opposite sense.

The arrangement can be so adapted that at a looser coupling, after reaching the critical coupling state, the feedback will be increased such that the two circuits remain critically coupled despite the variation of the actual coupling. In this way it is accomplished that the sensitivity is the most favorable one that can be attained and that at the same time the most favorable selectivity exists for this case. If, however, greater importance is to be attached to a higher selectivity, though with a loss in sensitivity, the feedback may be such that it increases at a smaller rate than the rate of decrease of the coupling so that the coupling is to an increasing degree carried out below the critical state. The conditions may also be so chosen that the sensitivity remains constant during the control of the band-width, since a loss due to a looser coupling can be compensated for by a higher feedback. Finally, the arrangement may also be so adapted that at a looser coupling the feedback already increases at such a high degree before reaching the critical coupling state that an excessive coupling appears. In this case it can be accomplished that the band-width remains constant at a certain height of the resonance curve while the steepness of the flank varies.

The mode of structure according to Figure 1 has the further advantage of avoiding practically any detuning since the position of the main coils L1 and L2 relative to the shielding does not vary, and since the feedback coil R is very small. In an experimental model of a band filter for an intermediate frequency of 490 kc, the coils were as follows: the number of turns of L1 was 180 windings, K had 15 windings, R had 4 windings and L2 had windings.

The parts indicated in dotted lines in Figure 1 represent the iron cores movable for adjustment. In order to avoid detuning they are preferably so arranged that they do not protrude beyond the inner sides of the coils so that there fore couplings too close with the movable coils cannot appear.

Also other modes of practicing the invention are possible. Figure 3 shows such a mode. The coil L1 (left) is fixed, while the coil L2 can be tilted. The feedback coil R. is likewise fixedly secured. When the couplingv of the coils L1 and L2 is rather loose (Figure 3 right) the coupling between the coil L2 and the feedback coil R becomes closer and therefore the frequency band permitted to pass will be narrower.

The invention can also be used for instance in an input filter, also where the selectivity is automatically controlled by means of a control potential through electrical means or electrodynamic means, and also where the feedback circuit and the band filter circuit are spacially separated.

I claim:

1. In combination with a high frequency signal energy transmission tube having input and output electrodes, a signal-tuned resonant input circuit, a second signal-tuned resonant circuit reactively coupled to the said input circuit, said second circuit being connected to said input electrodes, reactive means coupling said output electrodes to said second circuit thereby providing a feedback path for signal energy to said input electrodes, and means for simultaneously adjusting the magnitudes of said two reactive couplings in opposite senses whereby the degree of signal feedback varies directly with the degree of selectivity of said coupled resonant circuits.

2. In combination with a first resonant circuit tuned to a desired signal frequency, a signal transmission tube having a signal-tuned resonant input circuit and a signal output circuit, a link couplin coil reactively coupling said resonant input circuit with said first resonant circuit, a signal feedback coil reactively coupling said output circuit to said input circuit, and means for concurrently adjusting the magnitudes of the link and feedback coupling in opposed senses 10 whereby the degree of signal feedback varies inversely with the pass band width of said coupled resonant circuits.

FRIEDRICH KREIENFELD. 

